A ProMED-mail post is a program of the International Society for Infectious Diseases

Date: 28 Jan 2010
Source: Caller.com [edited]

Rare horse disease affects horses in 13 states

King Ranch, Texas, is the epicenter of a months-long outbreak of a deadly horse disease rarely seen in the United States that kills as many as 20 percent that it infects. As of 20 Jan 2010, 364 cases of equine piroplasmosis had been confirmed. Of those, 289 are on King Ranch. The rest are scattered across Texas, Alabama, California, Florida, Indiana, Louisiana, Minnesota, North Carolina, New Mexico, New Jersey, Tennessee, Utah and Wisconsin, according to the World Animal Health Information System.

A South Texas ranch, identified by the Texas Animal Health Commission as the outbreak's source, has sold horses with equine piroplasmosis in 15 states since 2004. Jack Hunt, the CEO of King Ranch, confirmed the outbreak started on the ranch.

Horses, donkeys, mules and zebras are susceptible to the disease, which is caused by 2 parasitic organisms. More severely affected animals can have fever, anemia, jaundiced mucous membranes, swollen abdomens and labored breathing.

"It will kill a horse," said Mike Vickers, a Brooks County veterinarian and commissioner on the Texas Animal Health Commission. "It's very, very serious."

No horses have died, officials believe. The ranch's 300-plus horses have since been quarantined. Piroplasmosis had never been seen in Texas and rarely had been found in the United States, according to the Texas Animal Health Commission, the state's livestock and poultry health regulatory agency. It is prevalent in 90 percent of the world and commonly found in Mexico.

Once a horse is infected, the parasitic organisms remain in the horse's system permanently, making the horse a potential carrier. It does not affect humans or other non-equine mammals. Ticks usually transmit the disease to horses, but it also has been spread from animal to animal by contaminated needle. There is some concern that it might be spread by biting horse flies, Vickers said.

Hunt, who has been in the ranching business for 35 years, said he had never heard of the disease when it was discovered in October 2009.

A total of 8 other ranches in Jim Wells, Kleberg, and Brook counties have been quarantined and tied to the initial outbreak, said James Lenarduzzi, a veterinarian with the Texas Animal Health Commission. Horses from ranches adjacent to King Ranch will be tested in coming weeks to determine if they are infected.

The 825 000-acre King Ranch includes most of Kleberg and Kenedy counties and portions of Brooks, Jim Wells, Nueces and Willacy counties. It is renowned for its horses, including 1946 Triple Crown winner Assault and 1950 Kentucky Derby and Belmont Stakes winner Middleground.

Though the ranch still has a horse breeding program, no horses have been sold since the quarantine, Hunt said.

The Texas Animal Health Commission issued its 1st directive on the South Texas-based infection 20 Oct 2009, noting that the disease had been confirmed on an undisclosed ranch. Canada promptly banned imports of Texas horses, though later relaxed the restrictions. A total of 10 states have stringent restrictions in place that call for testing and other controls before a horse can be imported from Texas.

State Rep. Yvonne Gonzalez Toureilles, D-Alice, who chairs the House Committee for Agriculture and Livestock, got involved this week after several South Texas ranchers complained that King Ranch has kept its name away from the outbreak, which started in October 2009.

Hunt said King Ranch self-reported the infection, which was required by law, and has worked openly with state and federal agencies since. "We are putting a lot of resources and energy into trying to figure out a way to take care of the problem," Hunt said. "What we don't do is cover up stuff, which we have been accused of in this case."

The state has 1 million horses. Owners, family members and volunteers spend USD 3 billion per year attending competitive events with more than 250 000 horses, according to a Texas A&M University report. And horse owners have more than USD 13 billion invested in barns, towing vehicles, trailers, tack and related equipment and spend more than USD 2.1 billion annually to maintain their horses.

Some South Texas ranchers are angry that the state and federal government have been tight-lipped on the disease's origin, said Lavoyger Durham, who manages the 13 000-acre El Tule Ranch near Falfurrias for Brown and Root heiress Nancy Brown Negley.

Lenarduzzi met with Durham and about 25 fellow South Texas ranchers Thursday [28 Jan 2010] to discuss the disease but would not say where it started, which Lenarduzzi said is standard operating procedure.

Gonzalez Toureilles said she will meet with Texas Animal Health Commission officials by Monday [1 Feb 2010] to make sure the outbreak is being handled correctly.

King Ranch also is working with the U.S. Department of Agriculture and some of the nation's top epidemiologists on experimental procedures to remove the parasite from a horse's system, Hunt said. "They have sent great people to work on this project, and we have had lots of interaction," Hunt said. "It's just a process we are all going to have to go through. It's not pleasant for anybody affected by it."

[Byline: Jaime Powell]

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[Equine piroplasmosis results from infection by the protozoa _Babesia caballi_ or _B. equi_ (phylum Apicomplexa). The 2 organisms may infect an animal concurrently.

Equine piroplasmosis is a tick-borne protozoal infection of horses. Piroplasmosis may be difficult to diagnose, as it can cause variable and nonspecific clinical signs. The symptoms of this disease range from acute fever, inappetence, and malaise, to anemia and jaundice, sudden death, or chronic weight loss and poor exercise tolerance. The disease may be fatal in up to 20 percent of previously unexposed animals. The tick vectors exist in the United States, and epidemics of piroplasmosis were seen in Florida in the 1960s.

The incubation period for _B. equi_ infections is 12 to 19 days, and infections are more severe. For _B. caballi_ infections, it is 10 to 30 days.

The clinical signs of piroplasmosis are variable and often nonspecific. In rare peracute cases, animals may be found dead or dying. More often, piroplasmosis presents as an acute infection, with a fever, inappetence, malaise, labored breathing, congestion of the mucus membranes, and small, dry feces. Anemia, jaundice, hemoglobinuria, sweating, petechial hemorrhages on the conjunctiva, a swollen abdomen, and posterior weakness or swaying may also be seen. Subacute cases may have a fever (sometimes intermittent), inappetence, malaise, weight loss, signs of mild colic, and mild edema of the distal limbs. The mucus membranes can be pink, pale pink, or yellow, and may have petechiae or ecchymoses. In chronic cases, common symptoms include mild inappetence, poor exercise tolerance, weight loss, transient fevers, and an enlarged spleen (palpable on rectal examination). Foals infected in utero are usually weak at birth, and rapidly develop anemia and severe jaundice.

In acute cases, the animal is usually emaciated, jaundiced, and anemic. The liver is typically enlarged and dark orange-brown. The spleen is enlarged, and the kidneys are pale and flabby. Petechial hemorrhages may be seen in the kidneys, and subepicardial and subendocardial hemorrhages in the heart. There may also be edema in the lungs and signs of pneumonia.

The differential diagnosis for piroplasmosis includes surra, equine infectious anemia, dourine, African horse sickness, purpura hemorrhagica, and various plant and chemical toxicities.

Equine piroplasmosis can be diagnosed by identification of the organisms in Giemsa stained blood or organ smears. _B. caballi_ merozoites are joined at their posterior ends, while _B. equi_ merozoites are often connected in a tetrad or "Maltese cross." Organisms can often be found in acute infections, but may be very difficult to find in carrier animals. In carriers, thick blood films can sometimes be helpful.

Because _Babesia_ organisms can be difficult to detect in carriers, serology is often the diagnostic method of choice. Serologic tests include complement fixation, indirect fluorescent antibody (IFA), and enzyme-linked immunosorbent assays (ELISA). The IFA test can distinguish between _B. equi_ and _B. cabali_.

Other methods of diagnosis include DNA probes, in vitro culture, and the inoculation of a susceptible (preferably splenectomized) animal with blood from a suspected carrier. In addition, pathogen-free vector ticks can be fed on a suspect animal, and _Babesia_ identified either in the tick or after the tick has transmitted the infection to a susceptible animal.

Disinfectants and sanitation are not generally effective against the spread of tick-borne infections. However, preventing the transfer of blood from one animal to another is vital.